-LRB- CNN -RRB- -- The king of the South Pacific nation of Tonga died `` peacefully '' Sunday at a hospital in Hong Kong , a Tongan government official said Monday . He was 63 .

A cause of death has not been released by the government .

`` Tonga has just woken up to the sad news of the passing of King George Tupou V , '' said Paula Ma'u , an official in the Ministry of Information and Communication . `` We are all in mourning . ''

Ma'u said Crown Prince Tupouto'a Lavaka , heir to the throne , was with the king `` just before he passed away . ''

Pesi Fonua , editor of Matangi Tonga online news website , said the Oxford-educated king was known for his world travel and spending habits , but was also respected for his efforts to bring democratic reforms and modernize Tongo .

`` This king brought in things like mobile phones and other advances that we could n't dream would come to Tonga , and his push for democracy made a big impact on the people here , '' Fonua said .

However , he said , Tongans had `` mixed feelings here in the community '' about the king .

`` He lived a bachelor life , always a single man , and he traveled a lot around the world and spent money . He brought us in some ways forward into the 21st century , but some people have different -- not as good -- views on him . ''

Australian Prime Minister Julia Gillard expressed her condolences in a statement Monday , crediting George V with guiding `` his country through a critical process of constitutional change towards the establishment of a constitutional monarchy . ''

Tonga , with a population of 106,000 , is the only monarchy that remains in the Pacific . George V ascended to the throne after the death of his father in September 2006 and quickly promised to speed up government reforms demanded by the people .

`` Let us rebuild a new capital and a new Tonga , '' George V said in 2006 , a week after a pro-democracy rally in the capital city of Nuku'alofa led to riots that left eight people dead and the central business district in ruins .

In 2008 , he announced he was giving up most of the near-absolute power that his family held for centuries and allowing the prime minister to guide the day-to-day governmental affairs .

Tonga is an archipelago of 171 islands directly south of Western Samoa . Less than a third of the islands are inhabited . The present dynasty was founded in 1845 after the Tongan islands were first united .

CNN 's Brian Walker contributed to this report .

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NEW : The king helped modernize Tongo and push for reforms , a Tongan news editor says

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A cause of death has not been released

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King George Tupou V had been monarch since 2006

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Tonga is the only monarchy that remains in the Pacific